In seats of land and air vehicles, mechanisms called "articulations" are increasingly used. These mechanisms include a reducing element for positioning either seat back or the seating portion. In the case of the seat back these mechanisms being each made of a fixed flange rigidly connected to the seating portion armature while a mobile flange is rigidly connected to the lower portion of the back armature of this seat.
These flanges comprise inside circular toothings with a different number of teeth. The circular toothings are relatively driven by means of a double satellite rolling on the aforementioned toothings by means of a cam having a periphery which is provided with a roller bearing placed in a recessed central portion of the satellite. This cam is in turn driven by a driving shaft controlled either manually or by means of a motor so that the inclination of the seat back with respect to the seating portion can be adjusted according to the wish of the passenger.
In the case where such reducing mechanisms, called "round articulations", are placed underneath the seat in order to adjust the position of the seating portion, the fixed part is rigidly connected to the base support of the seating portion; and the mobile part of the arms acts on the lower part of the armature of the seating portion in order to adjust the position of the seating portion.
Generally, the fixed and mobile flanges are attached to the members forming the fixed armature and the mobile armature either by means of bolts or by means of rivets placed at 120.degree. with respect to one another on the outer periphery of these flanges so that mounting of these round articulation mechanisms on the seats will be rapid and without problem.
Due to the manufacturing tolerances (in particular to the unavoidable ovalization of the various toothings which are formed most often by a fine cutting operation), and also due to the wear of these toothings, clearances will appear which impart a slight wobble either to the seating portion or to the seat back. Attempts have been made, by different means, to obviate these clearances but, till now, these mechanisms are ineffective and costly, and require a mounting operation which is sometimes difficult to carry out on an automatic machine.
This is the reason why a study has been made to provide, by opposite cones, a take up of the eccentricity of the toothings of the flanges and toothings of the satellite where there is a hard point caused by a combination of the abovementioned clearances.
There is thus obtained by a simple mechanism, a reduction of the eccentricity which occurs when a hard point is passed and therefore the clearances are taken up, thus avoiding the hereabove mentioned disadvantages.